Electrical testing system



Jan 21, 1947, w, c, RHEUBOTM 2,414,609

1 ELECTRICAL-TESTING SYSTEM Filed 00;- 5, 1944 2 Sheets-Sheet l Selector 5 Q INVENTOR Q I Wifiheubqtwnv' ATTORNEY 1947. w. c. RHEUBOTTOM 2,414,609

ELECTRICAL TESTING SYSTEM Filed 001:. 5, 1944 2 Sheets-Sheet 2 IN VEN TOR WC, Rh ea 6 0t zzmm ATTORNEY Patented Jan. 21, 1947 UNITED STATES PATENT OFFICE ELECTRICAL TESTING SYSTEM Willard C. Rheubottom, Norfolk, Va., assignor to American Telephone and Telegraph Company, a corporation of New York Application October 5, 1944, Serial No. 557,287

ticularly, this invention relates to apparatus for determining the section of a transmission system that may be out of order.

In type K carrier systems, for example, a plurality of four-wire transmission systems are enclosed within a single cable, each four-wire systembeing divided into two pairs or lines, one pair or line serving to transmit the signals of a plurality of channels in one direction and the other pair or line serving to transmit the signals of a like number of channels in the opposite direction. Each pair or line of the four-wire system includes a plurality of repeaters of well-known type Which, in general, are spaced several miles from each other, each repeater being usually located at an unattended station. When trouble arises in one of the four-wire systems, it has hitherto been the practice to dispatch a repairman to the different stations along the route to locate the trouble and have it repaired. The practice of having the repairman travel from station to station along the route to locate the approximate position of the fault, of course, consumes agood deal of time and is quite costly.

It is proposed, therefore, to improve the practice of locating the section of any one of the various four-wire transmission systems that may be out of order by installing apparatus at the centralswitching point and at each of the various stations along the route to permit tests to be made to determine the faulty section. Each station along the route may have a step-by-step selector and relays, all of which may be controlled by switching apparatus at the central point. The apparatus at the central switching point may be operated to step all of the selectors at the stations along the route so as to select the particular four-wire system that is to be tested. The apparatus at the central switching point may also be operated to connect an impedance pad across both pairs or lines of the selected fourwire system at any one of the various stations so as to enable the attendant at the central switching point to perform tests to determine whether the fault may be found between the central switching point and the first station along the route, or in the section between any two adjacent stations. Thus, by progressively connecting impedance pads across the four-wire system at different points along the route, the attendant at the central station will soondetermine the partil 2 ticular section of the four-wire system that is out of order.

This invention will be better understood from the more complete description hereinafter following when read in connection with the accompanying drawings, in which Figure 1 illustrates one form of apparatus which may be employed to carry out the invention, and Fig. 2 illustrates a modification of certain of the apparatus-shown in Fig. 1 to permit automatic or continuous tests to be performed to determine which of the sections of the various four-wire systems are in-good condition and which are out of order. I

Referring to Fig. 1 of the drawingsthree of a plurality of four-wire systems are shown extending between acentral office 00 and three of a plurality of stations which are designated AA, BB, CO. The two-wire lines or pairs L1 and L1 comprise one of the four-wire systems, the lines or pairs L2 and L2 comprise another of the fourwire systems and the lines or pairs L3 and L3 comprise still another of the four-wire systems.

The pairs L1 and L1 are typical of each of the various four-wire systems, the pair L1 including repeaters A1,;A2 and A3, for example, which are located-at stations AA, BB and CC, respectively,

and are arranged to transmit signals in one -direction, while the other pair L1 of this fourwire system includes similar repeaters-A1',Az' and A3 located at the same stations and arranged to transmit signals in the opposite direction. The central ofiice equipment may include a dial DL, or other switching device, which may be operated to select anyone of the various four-wire systems to be tested, and another switch SW which may be operated to select the station at which a suitable impedance pad may be bridged across the selected four-wire system. The stations AA, BB, CC include selectors SA, SB and SC, together with impedance pads or networks NT1, NTz, NTa, respectively, and relay apparatus which will aid in operating the stationequipment.

Assume that there is trouble on the four-wire transmission system L1-L1', and that it is desired to locate the section of the system where the trouble may be found. The attendant at the central office 00 will first operate the dial switch DL to select the faulty four-wire system L1-L2. By dialing number 1, for example, a single pulse will be transmitted to relay ST1 to operate that relay at station AA. The closure of the contact of the lower outer armature of relay ST'r will cause the magnet MGi of the selector SA to be er inner armature of relay 'STi will cause current to flow to relay STz at station BB to energize the latter relay. The closure of the contact of the lower outer armature of relay T2 will likewise energize the magnet MGz of selector SB at station BB and the closure of the contact of the lower inner armature of relay STz will cause current to flow to relay STs at station CC to operate that relay. The closure of the contact of the lower outer armature of relay ST3 will cause the magnet MGe of selector SC to be energized, and so on. As soon as the contact of the dial switch DL at the central ofiice CO is opened, the relay ST1 wil1 be released. This will release magnet MGl and cause the selector SA at station AA to step to its terminal number 1. The release of relay ST]. will likewise release relay STz, thereby deenergizlng the magnet MGz and causing the selector SB at station BB to be advanced to its terminal number 1. The release of relay STz will in turn release relay ST; and cause the deenergization of magnet MGs, whereupon the selector SC at station CC will be advanced to its terminal number 1.

It will now be observed that at station AA the tip and ring conductors of line L1 are connected through terminals numbers 1 of arcs l and 2 of selector SA to the upper outer and upper inner armature of relay LT1, respectively. At the same time the lower inner and lower outer armatures of relay LT1 are connected through the brushes of the arcs 3 and 4 of the same selector and their terminals number 1 to the tip and ring conductors of line L1, respectively. As relay LT1 is normally unoperated, the circuit between the pairs L1 and L1 of the four-wire system selected by selector SA will still remain open.

Moreover, the same four-wire system of pairs Lrand L1 will also be selected at station BB and be prepared for subsequent tests. So at station CC. 7

Should the attendant at the central oflice CO now desire to test the section of the selected four-wire system L1-L1' between the central office CO and station AA, he will move the switch SW to its terminal a. This will cause relay LTl at station AA to be operated. The operation of relay LT1 willconnect the network NT1 between the upper two armatures of the relay LT1 and its lower armatures. The network NT1 will now be bridged across the pairs L1--L1' of the selected four-wire system. The attendant may now listen to the signals, if any, flowing over line L1 from the central ofiice CO to station AA, then through the network NTi, and back over the portion of the line L1 between the same station AA and the central office CO and observe whether the signals are of the desired level. On the other hand, the attendant may connect to line L1 a generator of alternating current, such as A. C. of some predetermined frequency which may not interfere with signaling over the system, and. receive over line L1 the current of generator AC at the indicating device SR. If the current received is of insufiicient amplitude, the receiving device SR will indicate that fact to the attendant. If the received signals or alternating current is not at the required level, the trouble may then be ascribed to the section of the four-wire system between the central ofiice CO and station AA, and the attendant may then dispatch a repairman tothis section of the system to make the necessary repairs.

If the section of the system extending to station AA is in good condition, the attendant at the central'ofiic e CO will then operate the switch SW to its position b. As soon as switch SW leaves contact a, relay LT1 releases, removing the network NT1 from the circuit. The closure of contact I) will now cause the operation of relay LT; at station BB and thereby bridg the pad NTz across the pairs L1 and L1 of the same fourwire system at station BB. The attendant may then connect the generator AC and the receiver SR across the pairs L1 and L1, respectively, as before, and determine whether the received current is of the desired amplitude. If the level is insufiicient, the attendant will then fix the position of th fault as being in the section of the four-wire system L1-L1' between stations AA and BB.. Thus, by operating the switch SW to any of its terminals the attendant may bridge the impedance pad located at any one of the various stations across the selected four-wire system and proceed to determine the section of the system that is in trouble.

When the trouble 'on the selected system has been located the attendant will then return the switch SW to its initial position 0', and operate the dial mechanism DL to return the step-bystep selectors at the various stations to their normal positions. This may be done by the dial mechanism shown, for example, or by any other apparatus well known in the art.

If the attendant desires to select and test the four-wire system Ila-L3, for example, he may operate the dial apparatus DLby dialing number 3 and thereby step all of the various selectors SA, SB, SC to their terminals number 3. The four-wire system L3--L3' having been selected, the attendant will then connect any one of the various pads NTl, NT2, NT3 tions AA, BB, CC, respectively, across the selected four-wire system La-Ls'. He may then send current from the generator AC over line L3 and observe whatever response is available at the receiver or indicator SR. By following this procedure, the attendant will readily determine the particular section of the selected four-wire system L3-'I.s that may be in trouble.

systems hav been shown for illustrative purposes and that in a carrier system of the type K type many such systems may be included within a single cable, all of which may be tested by the apparatus of this invention. It will be similarly understood that only three stations AA, BB and CC have been shown, but that there may be many such stations between the central office CO and a similar central office (not shown) some distance away, all of which would be controlled from a single station such as CO.

Fig. 2 illustrates a modification of the apparatus at the central office C0 of Fig. 1, the modification being designed to enable tests of the conditions along the different sections of the various four-wire systems to be made continuously. Two rotors ARI and AR2 may be coupled to each other by gears, such as (3R1, or by other means of wellknown type, so that the rotor ARz may rotate through several revolutions while the rotor AR1 travels throughbutone revolution. The rotor ARI may contact a plurality of segments, two of which correspond to each of the various four-wire systems. Ten pairs of such segments are shown on the drawings, the segments S611 and SGn corresponding to the four-wire circuit L1-L1', segments SGz and SG12 corresponding to the fourwire circuit L2L2', segments 8G3 and SGn corresponding to four-wire circuit La-La, etc. The rotor ARz may progressively contact segments at sta- It will be understood that only three four-wire arrests sca, S'Gez, SG'EII'," etc; each of-which' corresponds to one; of the various stations, such as AA, M33,-

or CC, etc:, ofFig: 11; and twelvesuch segments aresh'own associatedwith rotor ARz. In-*the*il-" lustration given, the rotor'ARz will b required to travel through one revolution 111' thetime required for'th'e rotorARr to travel through one-tenth of a revolution.

When both rotors'AR1 and -AR2 are started-in therebyreleasingrelay STi. This will be followedby the advance of selectorsSA, SB, SC, etc., of Fig. 1 to their respective terminals number 1 as already explained. When rotor AR1 contacts segment SGn, the relay BB1 will be operated over a circuit completed from battery through the rotor AR1 and its segment SG11, lamp LP1, the winding of relay BB1 and ground. The closure of the upper make contacts of relay BB1 will connect the generator AC1 across the line L1 at the central oflice CO. The closure of the lower make contacts of relay BB1 will connect a tuned circuit TC in series with the winding of a relay CR1 across the line L1 at the central oflice CO. The tuned circuit TC1 may be resonated at the frequency of the current of generator AC1. The relay CR1, which receives the current traversing the tuned circuit TC1, will control an indicating device, such as lamp LP11.

As soon as the rotor ARZ has contacted segment SGzz, relay LT1 of Fig. 1 will be operated in the manner already described, to bridge the network NT1 across the lines L1 and L1 of the first fourwire system at station AA. Current will then flow from the generator AC1 over the line L1 of station AA, then through the network NT1 (of Fig. 1) and back over the line L1 through the tuned circuit TC to the winding of relay CR1. If insufficient current traverses the winding of relay CH1, the latter relay will remain unoperated, thereby illuminating lamp LP11. The simultaneous illumination of lamps LP1 and LP11 will indicate that there is a fault in the section of the four-wir system between the office CO and station AA. If there is no fault in this section, then lamn LP1 will alone be illuminated.

While the rotor AR1 is still in contact with segment SG11, the rotor ARz will be advanced to segment SG22 to operate relay LTz of Fig. 1. This will bridge the network LTz across the lines L1 and L1 of the same four-wire system at station BB. The current of generator AC1 will now flow over the line L1 of this four-wire system to station BB and back again to the central ofiice CO, as already described, to determine whether a fault may be present in the section between stations AA and BB. The rotor ARz will then continue through its cycle while rotor AR1 remains in contact with segment SGu, and the various sections along the route will be tested for a fault.

At the completion of the first revolution of rotor APJZ, the rotor AR will then successively contact segments 8G2 and SGm to again make and break the circuit of relay ST1 of Fi 1. thereby stepping the various selectors SA. SB, so, etc.,

to their terminals number 2. The rotor ARz will then conti ue throu h its next cycle to bridge networks NT1. NTz. NT3, etc., progressively across the second four-wire system L2L2' at the various stations AA, BB, CC, etc, respectively, to perform that networks-NT1', N'I'z, NTs' 6. similar tests on all sections I of the four -wir'e system L2L2'.- Thus; all sections of the various four-wire s'ystem'willbe tested in succession and this cycle will be repeated. It will be understood may be designed to presentequalor unequal loss values throughout, or these networksmay be designed to present diminishing loss values corresponding to their increaseddistances from oflice CO; as may be 1 required;

The arrangement of this invention is not to be construedas limited to a carrier system, norto a system-which may haverepeaters at various points along the line. The'apparatus of this invention is generally applicableto all types ofcircuits, includingtelegraph circuits; voice frequency circuits, and power circuits, to'determine the lo-- cation of a fault in any section of any of these various circuits.

While this invention has been shown and described in certain particular embodiments merely for illustrative purposes, it will be understood that the general principles of this invention may be applied to other and widely varied organizations without departing from the spirit of the invention and the scope of the appended claims.

What is claimed is:

1. Testing apparatus for determining the section of a four-wire system that may be defective, comprising a plurality of impedance pads, each positioned at a difierent point along the system, and means for selecting ony one of said pads and bridging it between the two pairs of wires of said system, whereby current flowing over one of said pairs of wires Will traverse the bridged pad and return over the other pair.

2. Testing apparatus for determining the section of a four-wire system that may be defective, comprising a plurality of impedance pads each of which is positioned at a difierent point along the path of the system, means for selecting any one of said pads and bridging it between the two pairs of wires of said system, means for transmitting current over one of said pairs of wires, through the selected path and back over the other of said pairs, and means for indicating the magnitude of the returned current.

3. Testing apparatus for locating the section of a four-wire system that may be defective, comprising a plurality of impedance pads each of which is positioned at a different point along the system, means for successively connecting the various pads between the two pairs of wires of said system. means for transmitting current over one pair and through the pad connected to the system and back over the other pair, and means for determining whether the magnitude of the returned current exceeds a predetermined value.

4. Testing apparatus for a plurality of fourwire systems all traversing a common route passing through a plurality of different points, comprising means for selecting any desired one of said four-wire systems at all of said points, a plurality of impedance pads each of which is located at one of said points, means for successively connecting the various pads between the two pairs of wires of the selected system, means for transmitting current over one pair of wires of the selected system and through the pad connected to said system and back over the other pair of wires of the selected system, and means for indicating whether the magnitude of the returned current exceeds a predetermined value.

. ;5, In a testing system for a plurality of fourwirepircuits all of which are routed through a plurality of stations, each four-wire circuit including two pairs of wirestransmitting currents in opposite directions, the combination of a plurality of step-by-step selectors, a plurality of networks, one selector and one network being located at each station, means for stepping all of said selectors equally to select any one of said four-wire circuits, means for selecting any one of said net-works and bridging it across the two pairsof the selected four-wire circuit, and means for determining whether the impedance of the selected four-wire circuit and the selected networkexceeds a predetermined value.

6. The combination of a plurality of four-wire circuits enclosed in a common cable, the route of which passes through a plurality of difierent stations, each four-wire circuit including two pairs of wires transmitting currents in mutually opposite directions, a plurality of selectors, a plurality of networks, one selector and one network being located at each station, means for operating all of said selectors so as to select any desired four-wire circuit at all of said stations, means for bridging the network at any desired station across the two pairs of wires of the selected four-wire circuit, and means for determining whether current transmitted over one pair ofwires of the selected circuit, through the bridging network and backover the other pair of wires of the selected circuit is above a predetermined value.

WILLARD C. RHUEBO'I'IOM. 

